[PATCH] mmc: dw_mmc: Turn the card clock off at suspend time

[Andrew Bresticker]

Doug,

On Wed, Nov 19, 2014 at 11:30 AM, Doug Anderson <dianders at chromium.org> wrote:
> Andrew,
>
> On Wed, Nov 19, 2014 at 11:03 AM, Andrew Bresticker
> <abrestic at chromium.org> wrote:
>> Doug,
>>
>> On Wed, Nov 19, 2014 at 10:51 AM, Doug Anderson <dianders at chromium.org> wrote:
>>> Since the dw_mmc driver was first added to Linux it's had a TODO in it
>>> that we should turn off the card clock during suspend.  I have no idea
>>> for sure why it wasn't done originally, but if I had to guess I'd
>>> guess it was related to the lack of a common clock framework.  Let's
>>> do it now.
>>>
>>> There is no reason for the card clock to be left on during suspend and
>>> most systems will eventually turn it off anyway (when whole clock
>>> trees are disabled).  However, it's good to be explicit that it's
>>> disabled at the time that the MMC subsystem is disabled.
>>
>> Should the bus clock (biu) be disabled as well?
>
> Good question.  I'm slightly hesitant to turn biu_clk off in this
> patch, though.  Specifically interrupts are still enabled at this
> point in suspend.  I  guess most interrupts shouldn't be going off
> right now (nobody is accessing storage, right?), but I could imagine
> that a card detect or an SDIO interrupt at just the wrong time could
> cause our ISR to go off _after_ this function is called.  The
> interrupt handling function doesn't know to turn the BIU clock back on
> so you'd get a hang.

Perhaps interrupts should be disabled as well across suspend/resume,
like the sdhci-based hosts do?  Would would happen if we tried to
service an interrupt with the ciu clock disabled?